The present invention relates to an ink jet device comprising an ink reservoir and a dispenser for ink pellets, wherein the dispenser comprises a sluice for discharging the pellets one by one into the ink reservoir.
In an ink jet device, such as an ink jet printer, an ink reservoir is incorporated in the printhead or in a separate cartridge and serves to accommodate a certain amount of liquid ink which is to be supplied to a nozzle system of the printhead. In case of a hot melt ink jet device the ink reservoir is heated in order to keep the temperature of the ink above its melting point, e.g., at a temperature of about 100xc2x0 C. or more. Research Disclosure Bulletin, March 1999, No. 41973, pages 374 to 376 discloses an ink jet device in which hot melt ink can be supplied in pellet or tablet form. The dispenser used for supplying the ink tablets one by one into the ink reservoir of the printhead may be mounted on the same carriage as the printhead so as to travel back and forth along the printing medium. Alternatively, the dispenser or at least an actuating mechanism thereof may be disposed stationarily above one of the end positions of the carriage, so that an ink tablet can be supplied into the reservoir each time the carriage has performed a complete stroke and stops in the end position.
The supply of ink in tablet form has the advantage that the amount of ink to be melted in the ink reservoir can be metered with high precision and, accordingly, the temperature of the molten ink within the ink reservoir can be kept stable.
The dispenser of known ink jet devices has a simple sluice mechanism of the type generally known in dispensers of candy. Such sluice mechanisms are, however, not fully reliable, and it may happen that the dispenser, although it has been actuated, fails to discharge a tablet. This may give rise to a shortage of ink, in particular in the case where the dispenser can be actuated only after each stroke of the carriage.
It is accordingly an object of the present invention to provide an ink jet device in which ink tablets can be supplied more reliably.
In order to achieve this object, there is provided an ink jet device wherein the dispenser comprises an output chamber for accommodating a single pellet discharged from the sluice, and a shutter for opening and closing the output chamber towards the ink reservoir.
According to the present invention, the pellet or tablet which needs to be timely supplied to the ink reservoir is held readily available in the output chamber and can reliably be transferred into the ink reservoir, simply by opening the shutter. Simultaneously or at a later instant, the sluice mechanism is actuated in order to supply another single pellet to the output chamber. If the sluice mechanism fails, it can be actuated repeatedly until a pellet is discharged into the output chamber, so that the next pellet will be reliably available when it is needed.
As is generally known, the dispenser comprises a storage chamber for accommodating a number of tablets and a slide movably disposed in said chamber and forming the sluice mechanism together with a portion of a bottom wall of the storage chamber. Preferably, the output chamber is also formed by a portion of the bottom wall of the storage chamber and a portion of the slide, and the shutter is also formed by a portion of the slide of the sluice mechanism, so that the shutter and the sluice mechanism can be easily actuated in a single operation. More specifically, the shutter and the output chamber may form a second sluice which has essentially the same construction as the first sluice. The reason why the sluice mechanism is not fully reliable is mainly due to the fact that a plurality of tablets present in a supply passage above the sluice tend to become clogged in the supply passage. Since the second sluice will not receive more than a single tablet at a time, a reliable and fail-safe function of the second sluice is assured.
In a preferred embodiment, a sensor, e.g., an optical sensor, is provided for detecting the presence or absence of a tablet in the output chamber, and when no tablet is detected after the sluice mechanism has been actuated, a signal is generated for actuating the sluice mechanism once again.